Embodiments of the invention relate to sensing systems, particularly, to sensing systems having a 2-wire interface.
One type of sensing system in a vehicle uses Hall effect sensors to measure rotational velocities exhibited by electric motors. Hall effect sensors are typically placed near ring magnets of the motors to measure rotation velocities. When a motor armature rotates, poles (North and South) of ring magnets pass by the Hall effect sensors. In turn, rates at which the poles pass by the Hall effect sensors are measured.
Ring magnets often have a fixed number of magnetic poles that is generally predetermined when motors are constructed. Different motors have different ring magnets, and thus a different number of magnetic poles. As such, knowing the number of magnetic poles can assist in determining motor speeds, for example, by measuring times between output pulses generated by the Hall effect sensors.
In some instances, motors have two Hall effect sensors positioned to measure information such as direction and speed of the motor. For example, Hall effect sensors are placed near ring magnets such that outputs of the Hall effect sensors are phased 90 degrees apart. Placing Hall effect sensors 90 degrees apart allows one of the Hall sensors to sense information such as the speed of the motor, and the other Hall sensor to sense other information such as direction of the motor. The physical location of the Hall effect sensors provide an indication of an order of the output pulses, which in turn provides an indication of the direction of the motor.
Some motor sensing implementations use a sensor that incorporates two Hall effect sensors in a single package. These sensors typically have two outputs. One of the outputs is a pulse train that indicates a speed of the motor, while the other output indicates a rotational direction of the motor. For example, a high output voltage can indicate a clockwise rotation, and a low output voltage can indicate a counter-clockwise rotation of the motor. Outputs such as speed and direction of motors are subsequently communicated through some electrical wire connection interface to an electronic control unit for further processing. Some implementations use four-wire connections. In such cases, the first of the four-wire connections supplies a voltage to both Hall sensors; the second of the four-wire connections provides a ground for both Hall sensors; the third of the four-wire connections provides an output for speed information; and, the fourth of the four-wire connections provides an output for directional information. Other implementations use a three-wire connection interface. In such cases, one of the three-wire connections provides a ground for both Hall effect sensors, another connection acts both as an output for speed information and as a voltage supply for both Hall effect sensors, and the third connection acts as an output for directional information and as a voltage supply for both Hall effect sensors.